9 replies to this topic

[David Sugiman]

Dear all,

I was recently introduced to different types of vacuum producing equipment, thanks to worksheet that I received from Art.

In our plant, all our vacuum producing equipments are still utilizing steam jet ejector to pull vacuum. The equipments so far are reliable, don't give us a lot of problems, but then it's utilizing steam which becomes more and more expensive nowadays.

If I may ask, what are the more popular vacuum producing equipments that are being used in the industry nowadays? Is is still utilizing steam jet ejector or other types, such as liquid piston ring rotary pumps, positive displacement pumps, etc?

In terms of reliability, operating cost, are they more superior in comparison to steam jet ejector?

Thank you.

[dehn0045]

where I am working we are using liquid ring rotary type vacuum pumps. Our systems were not designed very well, so we see a lot of times the process liquid contaminates the seal oil and we see equipment failures. I am not 100% sure, but I think that the rotary vacuum pumps are best for very deep vacuum at relatively low flow rates. The operating costs and reliability will vary depending on design requirements.

[djack77494]

In terms of reliability, operating cost, are they more superior in comparison to steam jet ejector?

David,
While I don't know what would be best in YOUR particular situation, steam vacuum jets are widely used in industrial vacuum settings. They are robust, reliable vacuum producers, but they do have "character". The only way to truly determine what is the least expwensive solution in your situation is to perform a study where you examine steam ejectors and one or more competitive mechanical devices.
Good luck,
Doug

[riven]

Two questions!

One what is your capacity (this will invariable depend on your pressure as well). Jet ejectors are most suitable for large capacities >~30000 cubes/hr. Below or near these flows, an analysis is required. At levels significantly lower than this (<~5000 cubes/hr) you may well find better options from oil sealed or dry pumps depending on question 2.

Two what are your compatibility issues? Are you just evacuating or 'pumping' air or do you have other gases? What are your temperatures?

[David Sugiman]

Dear all,

Thanks so much for all the reply.

To reply on Doug comment, I have to admit that I haven't performed study yet, but intended to do it in the near future. The question that I posted here is in a way to provide with better understanding on this issue.

To answer riven's queries:
1. Flow rate is approximately 75kg/hr of air at 1.3kPa.

2. We do have other hydrocarbon gas as well, with maximum temperature of about 10 deg.C. As of now, using steam ejector, we can recycle condensate back to process.

[riven]

See attached. This is a very basic calculation for dry air (i.e. option 1). Do not be surprised if you find mistakes.

The steps are.
1.Calculate volumetric flow to see if comparison is warrented.
2. Select options
3. Calculate main operating costs for options. In this case these are stream for the ejector and electricity for the pumps. Remember the pumps will require more maintenance.

For the second option (hydrocarbons), stick with the ejector especially if the recycling is easy.

Attached Files

•  very_basic_vacuum_comparison.xls   161.5KB   87 downloads

[Ali66]

Hi Riven,
30 lb/h of steam per 2800 ACFM at 10 mm Hg abs. sounds too low.
Are we missing a factor of a 100?
Ali

[riven]

Hi Riven,
30 lb/h of steam per 2800 ACFM at 10 mm Hg abs. sounds too low.
Are we missing a factor of a 100?
Ali

Well spotted

[pawan]

Dear David
I just finished similar study & found that liquid ring vacuum pumps are not good due to frequent failures becasue balancing of gaseous & liquid forces are enecessary in these pumps & they do not save cost also significantly due to chilling requirement in low pressure operation of something like below 20 torr.

In your case U need ~5-10 torr with low capacity, U can easily start with dry vacuum pumps either scroll or srew type. We are using screw type for 7503/hr @ 1 torr. The financial impact for us was as below

Savings from steam ejectors - 25000$/yr
Additional investment required for Dry Vac Pump - 10000$
Payback - 06 Months

Total Investment for a Vac pump - 35-40000$
Total Investment for Ejectors - 25-30000$

They are very robust & useful. I am replacing my Ejectors one by one with them.

[David Sugiman]

Dear all,

Thanks so much for the information.